In most oil wells, the pumping is carried out by use of a reciprocating downhole pump that is supported by a pumping rod which extends from the pump to the earth's surface where it is connected to a reciprocating walking beam. The beam is provided with a counter balance weight to offset the weight of the rod, the pump and the fluid column. There are many variable factors involved in the operation for pumping equipment of this type. Various types of instrumentation have been developed to monitor the pumping operation and measure the parameters of such operation. Once such measurements have been made, it is often possible to make adjustments and optimizations to improve the pumping efficiency of the well. For some measurements it is necessary to know the position of the rod in the stroke of the pumping operation. This measurement has heretofore been made in a number of ways. One technique has been to use a spring-loaded rotating potentiometer connected to the rod or beam by a string or cable so that the potentiometer rotates with the up and down motion of the rod or walking beam. This produces a changing resistance that is proportional to the position of the rod. However, mechanical equipment of this type is awkward, expensive and subject to easy breakage. The position of the rod can also be determined by mechanical position switches, but these are also subject to wear, environmental damage and calibration difficulties.
An apparatus for measuring the position of a sucker-rod is described in U.S. Pat. No. 4,561,299 entitled "Apparatus for Detecting Changes in Inclination or Acceleration".
An apparatus which utilizes an accelerometer to measure course length in a wellbore is described in U.S. Pat. No. 4,662,209 entitled "Course Length Measurement". This device, however, does not measure pump rod position.
Thus, there exists a need for a method and a corresponding apparatus for determining the position of a pumping rod and to analyze other pumping system aspects during pumping operations in such a manner that is reliable, accurate, inexpensive, convenient and not significantly affected by wear and exposure.